The fishing is good at Alsop Lake these days.
Wyoming Game and Fish Department fisheries biologists surveyed the lake earlier this spring and reported Yellowstone cutthroat trout averaging about 19 inches and rainbow trout averaging more than 20 inches long. Their sample group included a 24-inch, six-pound rainbow. The lake also has a few Arctic grayling that measured about 14 inches long.
“Since 2016, we’ve had good survival and really good growth,” said biologist Steve Gale.
Alsop Lake experienced a die-off in early 2016, though it was restocked later that year, as it is annually, with 5,000 rainbows and 2,500 cutthroat. Since then, the fish have thrived and there haven’t been any other anomalous events, Gale said.
“We were really impressed with the conditions and the size of the fish just three years into it,” Gale said. “That’s some of the best growth that we’ve seen in the last three years from any of the plains lakes.”
Game and Fish biologists have been investigating the lake for potential threats to fish health, and that work is still underway. Gale said they’ve been monitoring the oxygen content of the water and measuring the temperature under the ice during the winter. They’re also monitoring the oxygen levels and temperature during the warmest summer months.
“We’re looking at potential changes to different water-quality variables at Alsop Lake that may have in the past affected fish survival, or may in the future,” he said.
The 2016 die-off wasn’t a traditional winterkill, Gale said, leading biologists to explore different causes. The water in the lake has been turbid for the last few years as well, though that might not be an issue that affects fish health.
“We’re trying to see if we can pinpoint any of the causes of the decreased water clarity and other potential issues that could affect fish survival,” he said.
Because of the turbid water, anglers might have a hard time luring fish onto their hooks, however, meaning they’ll have to work a little harder for that trophy catch.
“When people do catch a fish, it tends to be a really nice one,” Gale said.
Winterkill refers to the dying of fish in a body of water because of a lack of oxygen. Gelatt, Alsop and Meeboer are three plains lakes especially susceptible to the phenomenon, which occurs in shallow bodies of water during harsh winters.
When ice and snow cover a lake in the winter, sunlight can’t reach underwater plants, which produce oxygen through photosynthesis. Eventually, the plants die and start to decompose, which further reduces oxygen in the water to levels where fish suffocate.
The Laramie plains lakes, situated in shallow depressions carved by wind, are full of aquatic vegetation. That vegetation supports abundant insect life and in turn allows fish to grow quickly, making the lakes ideal bodies of water to stock with rainbow and cutthroat trout. But in the winter, too much vegetation taking up the available oxygen presents a threat to aquatic life.
Biologists have used a variety of methods to prevent winterkill on the plains lakes in recent years, including aeration to prevent ice build-up, a snow fence to prevent snow accumulation, plowing of the ice to allow more sunlight through and even a species of sterile carp in Gelatt that feeds only on vegetation.
Gale said they stopped running aerators at Alsop, thinking that the resulting mixing of the water might cause other issues.
They do purchase water once a year from a local rancher to fill the lake.
“That’s to keep water levels up and keep the oxygen levels up there,” Gale said.
He said anglers looking to drop a line in Alsop should go in the early morning or in the evening when temperatures are the coolest.
“This fall as things cool down should be another good opportunity for anglers to get out on the plains lakes and enjoy the big fish,” he said.
Alsop Lake has a two-fish daily creel limit and possession limit for trout. Anglers must use artificial flies and lures only, and all trout shorter than 16 inches must be returned to the water immediately.